'nonparallelism' is formed from the prefix 'non-' + 'parallel' + the noun-forming suffix '-ism'. 'non-' (from Old English/Old French/Latin use) means 'not'; 'parallel' ultimately derives from Greek 'parallēlos' meaning 'beside one another'; '-ism' comes from Greek '-ismos' via Latin/French to mark a condition or practice.

'parallel' comes from Greek 'parallēlos' (para- 'beside' + allēl(os) 'one another'), passed into Late Latin and Old French and then Middle English as 'parallel'. 'parallelism' developed in English by adding '-ism' to denote the condition or quality; 'non-' was later prefixed to negate that condition, forming 'nonparallelism'.

Originally the root idea meant 'lying side by side' (Greek), then extended to mean similarity or correspondence; 'nonparallelism' therefore initially simply signified 'not side by side' and has come to be used both in geometric senses and figuratively (e.g., lack of parallel grammatical structure).